Gemm, Not exact but close enough or my purposes. I find the measuring for tracking fabric in and out is pretty easy: length in inches x width in inches x 2 (front and back) divided by 1440 (which is approx 40 inches by 36 inches of usable fabric per yard).
For example if a quilt that measures 55 X 65 that equals 3575 square inches x 2 (front and back). This is a total of 7150 square inches used in the quilt. Divide by 1440 (square inches in a yard) and the quilt used approximately 4.96 (round to 5 yards) used for the quilt. I then add another half yard for binding which means I would have used 5.5 yards of fabric.
I found this calculation method on the mycarolinahome.com website. It looks so awkward when written out like above. The quicker calculation is: Length x Width X 2, divided by 1440 + 1/2 yard = fabric used per quilt.